The use of renewable energy sources for electricity production is known in the state of the art, among which wind energy is one of the most efficient. Wind energy enables production of electricity from wind by means of wind turbines. Said wind turbines consist basically of a tower, a nacelle that houses the electric generator and a rotor formed of at least one blade. The wind generator tower supports the nacelle and the rotor. In the case of large wind turbines, the towers may be manufactured from steel, lattice, reinforced concrete or a combination thereof, the latter comprising sections of different materials, for example, a lower section of concrete and an upper section of steel or lattice.
In the last twenty years the nominal power of wind turbines has gradually increased due to the increase in diameter of the rotor thereof, which in turn makes the use of taller towers essential. The increase in height can make it essential for the tower to comprise various sections therethrough which are disposed one on top of the other to form the tower and which in turn can be transported by road or rail. For example, in order to mount a 100-meter tower, five 20-meter tall stackable sections could be used, said dimensions allowing transport thereof by road and rail.
Further, in order to ensure that, while being taller, the towers are equally stable and rigid, one of the options is to increase the tower's transverse dimensions gradually from the top to the base. Said increase could imply new problems for transporting the sections and the usual solution consists of dividing them into longitudinal modules or dowels. The dimensions of the longitudinal modules enable transport thereof by road or rail.
The precision and quality of the dowels, particularly of the upper and lower flanks, determine section stacking precision and therefore tower verticality. In order to solve the stacking problems associated with lack of precision, flatness and parallelism of the sections flanks, the upper section is aligned over the lower section maintaining a space therebetween, in order to subsequently use a joining and filling material that absorbs the deviations with respect to the nominal value of the two sections. In general, the joining material is wet and requires curing time to eliminate the wetness, in such a manner that the joint acquires the adequate mechanical properties. This is known as “wet joint”, where the application of the joining material requires the assembly of formwork around the joint.
In the concrete tower assembly process, when the tower sections lack the required precision, as mentioned earlier, a joining material that absorbs the imperfections of both sections, particularly those of the bond flanks, must be used. This requires a long and expensive process. Said process comprises the following steps:                Disposing a section on the part of the tower already assembled, leaving a space between the two adjacent sections.        Aligning the section with the rest of the tower, maintaining the separation.        Assembling formwork throughout the joining area between sections.        Pouring the joining material or mortar.        Waiting for the joining material to cure and disassemble the formwork.        
As can be observed, the tower assembly process using this method is long and costly.
An alternative to this assembly process is the joint known as “dry joint”, which only comprises the steps of stacking sections and applying the joining means therebetween (bolts, post-tension cables . . . ), significantly simplifying and reducing tower assembly time.
In concrete tower assembly using the dry joint method, the transverse surfaces (upper and lower flanks) of adjacent sections that come into contact must have a flatness and finish such as to guarantee the correct contact therebetween and, therefore, adequate transmission of stresses between sections. It is also fundamental that the upper and lower flanks of each tower section, in addition to being parallel therebetween, are also perpendicular to the axis of the section, as this aspect determines the verticality of the tower once assembled.
In butt joints of this kind, very precise tolerances and surface finishes must be ensured in order for the joint to have good mechanical properties.
In order to achieve the required quality levels, both in wet joint solutions and dry joint solutions, but particularly in the case of the latter, high-precision moulds are required. To this end, the moulds are generally very rigid, as a large amount of material is used in the manufacture thereof in order to avoid deformations due to the weight of the concrete itself or to any other cause, in such a manner that the cost of the mould is very high. Also, the upper and lower flanks are delimited by side walls rigidly joined to the base or countermould of the moulds, due to which any deformation of the mould affects the orientation of the flanks.
By way of alternative, patent application WO2011/157659 A1 discloses a solution for achieving the required degree of precision that consists of mechanically rectifying the flanks of each section once manufactured. This additional process represents a cost overrun for the section.
An intermediate solution consists of applying on the upper flank of the lower section a layer of a high-viscosity joining material, such as resin or mortar, prior to carrying out the butt joint of the upper section. In this manner, the joining material fills any remaining spaces between the two flanks and dispenses with the need for formwork; however, this also requires extremely narrow section manufacturing tolerances.